Membrane bioreactors are one of several types of Activated Sludge Process wastewater treatment facilities designed to remove contaminants from domestic and runoff wastewater. This wastewater comes from residences, businesses, industry, and runoff water from rainfall or flooding. Wastewater treatment facilities remove organic and solid waste from water so that the water can be recycled back into the environment. A facility should be able to accommodate dry and wet weather flows and peak flows.
A membrane bioreactor (MBR) employs micro-filters (membranes) that separate clean water from solid waste and sludge. First, the water is biologically treated in an aerobic process by micro-organisms that consume the organic contaminants in the water and produce solid waste sludge. Then, the water is drawn through the micro-filters, which separate the water from the sludge. Typically, the clean water is pumped out of the micro-filters. The majority of the water (the “return activated sludge”) is recycled back to the aerobic process, and a smaller amount (the “waste activated sludge”) is processed for suitable disposal, such as at a landfill.
While membrane bioreactors provide an effective method for treating wastewater, they have some drawbacks. Many bioreactor designs contain several tanks and basins through which the wastewater flows in series, and as a result repair and maintenance of an individual tank requires a large portion of the bioreactor to be taken off-line. This can significantly reduce the operating capacity of the bioreactor. In general, a waste water treatment facility with n tanks should meet the design criteria with n-1 tanks in operation. Additionally, the bioreactor requires the wastewater to be recycled back through the different tanks multiple times for adequate treatment of the water. Some existing bioreactors use multiple, complex pipe systems, channels, and pumps to recycle and divert the wastewater as needed. These piping systems can be expensive to install and maintain. Also, membrane bioreactors operate at higher concentrations of Mixed Liquor Suspended Solids (MLSS) than other treatment facilities. The recycling rate of the wastewater from the MBR back to the aerobic zone is approximately three to five times greater than extraction of permeate (filtered water) through the membrane.
Accordingly, there is a need for an improved membrane bioreactor that can be more easily operated and maintained.